Melting unit for a moulding machine and a moulding machine

ABSTRACT

A melting unit for an injection unit of a moulding machine, includes a melting vessel, an induction coil surrounding the melting vessel at least in areas for the inductive melting of a conductive material to be arranged in the melting vessel. At least in that area where it is surrounded by the induction coil, the melting vessel has an irradiation area that is substantially permeable to an electromagnetic field, and has a delivery opening for the melted conductive material. The melting vessel consists of a non-metallic material at least in the radiation area and in that the melting vessel has an uninterrupted lateral surface.

BACKGROUND OF THE INVENTION

The invention relates to a melting unit for an injection unit of amoulding machine, an injection unit with such a melting unit, and amoulding machine with such an injection unit.

Generic melting units, injection units and moulding machines are foundin DE 10 2016 006 917 A1 and EP 3 075 465 A1.

In the state of the art the lateral surface of the melting vessel in theradiation area is interrupted in the form of a slit, in order to allowthe electromagnetic field generated by the induction coil to penetrateinto the radiation area. This is disadvantageous because it results inan inhomogeneous melting process for the conductive material (usuallymetal) to be melted and melted conductive material can leak from thisslit during the injection. A cooling of at least the material of themelting vessel surrounding the radiation area is imperative.

The object of the invention is to provide a generic melting unit, ageneric injection unit and a moulding machine in which at least one,preferably all, of the problems discussed above are avoided.

SUMMARY OF THE INVENTION

This object is achieved by a melting unit as described below, aninjection unit with such a melting unit, and a moulding machine withsuch an injection unit. Advantageous embodiments of the invention arealso described.

The radiation area is that area of the melting vessel which holds theinduction coil and in which the electromagnetic field generated by theinduction coil acts during operation. The injection area is that area ofthe melting vessel which includes the delivery opening and which isunder the influence of the injection forces resulting from the injectionpressure during operation.

The non-metallic material of the radiation area can be e.g. graphite,stone (without conductive components to any extent relevant for theformation of eddy currents), ceramic, ceramic alloy or glass.

The melting vessel is preferably formed as an elongate body,particularly preferably with a cylindrical or prismatic shape, which hasa chamber that is accessible from the outside via a delivery opening.

A metal or a material made of a metal alloy is preferably used as theconductive material to be melted.

According to the invention, the melting vessel has an uninterruptedlateral surface over its entire length (optionally apart from openings,closed during operation, for windows, sensors or the like). Due to theclosed design, the melted conductive material can be injected into thecavity at higher injection speeds, as it is impossible for meltedconductive material to leak, or even spurt out, from anywhere other thanthe delivery opening.

Through the use of a non-metallic material for the melting vessel atleast in the radiation area, the electromagnetic field of the inductioncoil can penetrate into the radiation area over the entire lateralsurface and the conductive material to be melted can heat uphomogeneously. Tests were able to demonstrate that less time was neededto achieve complete melting of the conductive material to be melted. Therisk of the conductive material to be melted bursting out is alsosubstantially reduced. A cooling of the radiation area is not necessary,as no relevant eddy currents form in the non-metallic material of themelting vessel.

The melting vessel preferably has substantially the shape of a tube witha continuous chamber, wherein one end of the tube forms the deliveryopening for the melted conductive material. The other end of the tubecan be used for the insertion of an injection plunger. The area of thetube extending away from the delivery opening forms the injection area.That area of the tube which is surrounded by the induction coil formsthe radiation area, where the melting of the conductive material to bemelted takes place. The injection plunger can be arranged outside theradiation area irrespective of the injection process. In this case, thechamber of the melting vessel, starting from the delivery opening, formsan injection area, a radiation area preferably directly adjoining thelatter and a storage area for the injection plunger preferably directlyadjoining that.

In one embodiment of the invention it is provided that the meltingvessel consists of a metallic material in the injection area andconsists of a non-metallic material in the radiation area. The metallicmaterial has a higher mechanical resilience, which can be important inthe area of the injection area. In other words, in this embodimentexample the tube is composed of an axial portion made of metallicmaterial (which has the delivery opening) and an axial portion made ofnon-metallic material (in which the induction coil is arranged over apart of the length and the injection plunger is arranged). It can beprovided here that in that area where the metallic material buttsagainst the non-metallic material it surrounds the latter in the form ofa sleeve.

In an alternative embodiment of the invention it is provided that themelting vessel consists of a non-metallic material up to the deliveryopening (preferably the melting vessel as a whole). Here there is nopoint of abutment between injection area and radiation area. Amechanical strengthening structure is preferably provided at least inthe injection area.

A dispensing device can be provided, by which a mould-release agent canbe applied to the inside of the melting vessel at least in the radiationarea, wherein a chemical reaction between the melted conductive materialand the non-metallic material of the radiation area can be prevented bythe mould-release agent. A contact and resultant undesired chemicalreactions of substances possibly contained in the conductive material tobe melted with the inside of the melting vessel can hereby be avoided.

BRIEF DESCRIPTION OF DRAWINGS

Embodiment examples of the invention are discussed with reference to thefigures. There are shown in:

FIGS. 1a,b are sectional representations of a detail of a firstembodiment of a moulding machine according to the invention and a frontview thereof;

FIGS. 2a,b show a first and a second stage of a loading process usingthe melting unit of FIG. 1;

FIGS. 3a-c are, respectively, a side view of a melting vessel of asecond embodiment of a melting unit according to the invention, a frontview thereof, and a sectional view;

FIG. 4 shows the application of a mould-release agent to an inner wallof the melting vessel; and

FIG. 5 is a schematic view of a moulding machine according to theinvention

DETAILED DESCRIPTION OF THE INVENTION

A moulding machine 1 according to the invention is representedschematically in FIG. 5. A movable moulding platen 14 (the drive formoving the movable moulding platen 14 is not represented) and astationary moulding platen 13 are arranged on a frame 16. Rails forguiding the movable moulding platen 14 can be provided, but are notnecessary in every design.

The stationary moulding platen 13 and the movable moulding platen 14each carry one mould half 15. After the mould halves 15 have been closedby moving the movable moulding platen 14 onto the stationary mouldingplaten 13 until the mould halves 15 are in contact, the meltedconductive material can be injected into a cavity formed in the mouldhalves 15 through an injection plunger 11, which can be movedtranslationally back and forth by an injection drive 12. After apossible holding-pressure phase the melted conductive material cools andforms the desired moulded part. The moulded part can be removed from thecavity by means of the delivery device 10.

In this embodiment example the delivery device 10 for the conductivematerial 4 to be melted is mounted on the stationary moulding platen 13,but could also be arranged elsewhere on the frame 16 or next to theframe 16 independently of it.

In the embodiment example shown the injection is effected through thestationary moulding platen 13. Other configurations are conceivable,such as e.g. an injection between the moulding platens 13, 14 (L-shapedassembly arrangement or 90-degree arrangement of the injection unitrelative to the machine axis).

Details regarding embodiments of the melting unit, here formed by themelting vessel 2, the injection plunger 11, the injection drive 12, theinduction coil 3 and the delivery device 10 for the conductive material4 to be melted, can be derived from FIGS. 1 to 4. In the embodimentexample of FIGS. 1 and 2 the melting vessel 2 is formed in two parts.The embodiment example of FIG. 3 shows a one-part formation of themelting vessel 2. Independently of the design measures otherwise shown,the melting vessel 2 naturally always has a delivery opening 6 for themelted conductive material.

FIG. 1a shows a detail representation along the section A-A of FIG. 1bin the area of the melting vessel 2.

The melting vessel 2 is formed substantially tubular (with anuninterrupted lateral surface) and has at the left-hand end in FIG. 1a adelivery opening 6, which communicates with the mould half 15 (notrepresented) arranged on the stationary moulding platen 13. An opening,into which the injection plunger 11 is inserted, is arranged at theright-hand end in FIG. 1a . The state after the delivery of theconductive material 4 to be melted (here formed as a moulding blank) butstill before the conductive material 4 is melted is shown. The meltingis effected in a manner known per se (optionally after generation of avacuum in the melting vessel 2 by a suction device, not represented) bymeans of the induction coil 3, which is arranged along an axial portionof the radiation area 5. The induction coil 3 generates anelectromagnetic field, which induces eddy currents in the conductivematerial 4 to be melted. The Joule heat formed thereby melts theconductive material 4 to be melted.

The melting vessel 2 has an injection area 7, extending from thedelivery opening 6 in the direction of the radiation area 5, which inthis embodiment example extends directly to the radiation area 5.

The melting vessel 2 is formed from a non-metallic material (e.g.graphite, stone, glass, ceramic or ceramic alloy) in the radiation area5, in which the induction coil 3 is arranged. No, or at least norelevant, eddy currents are induced in this non-metallic material, whichis why no cooling of the melting vessel 2 is necessary in the radiationarea 5. The electromagnetic field can penetrate into the radiation area5 over the entire circumference of the uninterrupted lateral surface andhomogeneously heats the conductive material 4 to be melted.

In order to allow for high injection pressures, which can arise in theinjection area 7 immediately in front of the mould halves 15, in thisembodiment example the melting vessel 2 is formed from a metallicmaterial in the injection area 7. A tempering device for tempering(cooling or heating) the injection area 7 could be provided in theinjection area 7, but this is not imperative. It is advantageous that notempering device is necessary in any case in the injection area 5. Inthat area where it butts against the non-metallic material, the metallicmaterial surrounds the latter in the form of a sleeve (this is notstrictly necessary, but it increases the mechanical stability of themelting vessel 2).

In the embodiment example of FIG. 3 the melting vessel 2 is formed overits entire length from a non-metallic material such as graphite, stone,ceramic, ceramic alloy or glass. Here a mechanical strengtheningstructure 8 (for example a shrink sleeve) for the melting vessel 2 isarranged in the injection area 7. This serves to prevent damage to themelting vessel 2 by forces occurring during the injection in theinjection area 7 (which can result from injection pressures of up to1800 bar). Alternatively the melting vessel 2—at least in the injectionarea 7—could be formed sturdier than is necessary when a mechanicalstrengthening structure 8 is used. Alternatively or additionally,instead of a mechanical strengthening structure 8, a non-metallicmaterial with a sufficiently high mechanical resilience could be used.Depending on the choice of the conductive material 4 to be melted (e.g.in the case of aluminium) forces that are so large as to requireparticular measures in order to protect the melting vessel 2, consistingas a whole from non-metallic material, do not, in any case, occur duringinjection.

FIGS. 2a (section along B-B) and 2 b (section along C-C) show differentstages of a process of loading the melting vessel 2 with the conductivematerial 4 to be melted. The statements regarding the loading processapply to both embodiments of the melting vessel 2 discussed.

The moulding blank (generally: the conductive material 4 to be melted)is held on a gripper 17 in a tube 18 and inserted into the deliveryopening 6 via a robotic arm, not represented, of the delivery device 10(FIG. 2a ). The moulding blank is deposited by the gripper 17 in theradiation area 5 (FIG. 2b ).

After the delivery device 10 has left the area between the mould halves15, the mould halves 15 are closed. The air contained in the meltingvessel 2 can be removed by suction as required. Additionally oralternatively, the melting vessel 2 could be flooded with a protectivegas. In both cases the melted conductive material can be prevented fromreacting with oxygen contained in the ambient air.

The following statements apply to both embodiments discussed:

Contrary to what is represented, a window could be arranged in themelting vessel 2 in order to measure the temperature of the conductivematerial 4 to be melted through this window. It can thereby be ensuredthat the conductive material 4 to be melted is in fact completely meltedbefore injection. As an alternative or in addition to such a temperaturemeasurement, the necessary process variables (e.g. field intensity andexposure time of the electromagnetic field) can be determined by seriesof tests or model calculations.

Contrary to what is represented, the conductive material 4 to be meltedcould be inserted into the melting vessel 2 in a form other than that ofa moulding blank, e.g. in the form of a powder or granular material.

Contrary to what is represented, the delivery device 10 could also beformed as shown in EP 3 075 465 A1.

LIST OF REFERENCE NUMBERS

-   1 moulding machine-   2 melting vessel-   3 induction coil-   4 conductive material to be melted-   5 radiation area of the melting vessel-   6 delivery opening of the melting vessel-   7 injection area of the melting vessel-   8 mechanical strengthening structure for the melting vessel-   9 dispensing device for mould-release agent-   10 delivery device for the conductive material to be melted-   11 injection plunger-   12 injection drive-   13 stationary moulding platen-   14 movable moulding platen-   15 mould half-   16 frame of the moulding machine-   17 gripper of the delivery device-   18 tube of the delivery device

1. A melting unit for an injection unit of a moulding machine, comprising a melting vessel, an induction coil surrounding the melting vessel, at least in areas for the inductive melting of a conductive material to be arranged in the melting vessel, wherein at least in that area where it is surrounded by the induction coil the melting vessel has an irradiation area that is substantially permeable to an electromagnetic field, and a delivery opening for the melted conductive material, wherein the melting vessel consists of a non-metallic material at least in the radiation area and in that the melting vessel has an uninterrupted lateral surface.
 2. The melting unit according to claim 1, wherein the melting vessel consists of the non-metallic material up to the delivery opening, wherein it is preferably provided that a mechanical strengthening structure for the melting vessel is provided in an injection area adjacent to the delivery opening or extending up to the latter.
 3. The melting unit according to claim 1, wherein the melting vessel has an injection area, extending from the delivery opening in the direction of the radiation area, which consists of a metallic material, wherein it is preferably provided that the injection area extends up to the radiation area.
 4. The melting unit according to claim 3, wherein a tempering device for tempering the injection area is provided.
 5. The melting unit according to claim 1, wherein the non-metallic material of the radiation area is graphite, stone, ceramic, ceramic alloy or glass.
 6. The melting unit according to claim 1, wherein a dispensing device is provided, by which a mould-release agent can be applied to an inside of the melting vessel at least in the radiation area, wherein a chemical reaction between the melted conductive material and the non-metallic material of the radiation area can be prevented by the mould-release agent.
 7. The melting unit according to claim 1, wherein a delivery device for the conductive material to be melted is provided.
 8. The melting unit according to claim 6, wherein the dispensing device for the mould-release agent is arranged on the delivery device or formed by it.
 9. An injection unit for a moulding machine with at least one melting unit according to claim
 1. 10. The moulding machine with an injection unit according to claim
 9. 